Probing Hidden Symmetry and Altermagnetism with Sub-Picometer Sensitivity via Nonlinear Transport

TL;DR

This study uses nonlinear transport measurements to detect hidden crystal symmetry breaking and altermagnetism in Ca$_3$Ru$_2$O$_7$, revealing subtle lattice distortions and magnetic transitions beyond diffraction limits.

Contribution

It introduces nonlinear transport as a highly sensitive method to uncover hidden symmetries and magnetic phases in strongly correlated materials, surpassing traditional diffraction techniques.

Findings

Detection of lower-symmetry phase via nonlinear resistance below T$_S$

Observation of nonlinear Hall effect linked to symmetry breaking

Identification of lattice distortion (~0.1 pm) associated with magnetic transition

Abstract

X-ray and neutron diffraction are foundational tools for determining crystal structures, but their resolution limits can lead to misassignments, especially in materials with subtle distortions or competing phases. Here, we demonstrate the use of nonlinear transport as a complementary approach to uncover hidden crystal symmetries, using the strongly correlated Ca$_3$Ru$_2$O$_7$ as a case study. Below 48 K (T$_S$), where the magnetic moments of the antiferromagnetic phase reorient from the a- to the b-axis, leading to a pseudogap opening, our measurements, with support of DFT, reveal a previously overlooked lower-symmetry phase. This is manifested by the emergence of longitudinal nonlinear resistance (NLR) along the b-axis below T$_S$, providing direct evidence of combined translational and time-reversal symmetry breaking. This response also suggests a transformation from a conventional antiferromagnet into an altermagnet. The lower-symmetry phase arises from a subtle lattice distortion (~0.1 pm) associated with the magnetic transition at T$_S$, below the detection limit of conventional diffraction. Moreover, this NLR below T$_S$ is accompanied by a nonlinear Hall effect, both of which are enhanced by the large quantum metric associated with Weyl chains near the Fermi surface. Our findings demonstrate nonlinear transport as a sensitive probe of hidden symmetry breaking and altermagnetism, complementing and extending beyond the reach of traditional diffraction and spectroscopic techniques.